We propose to use plastic casts of the internal structure of dentine to determine: a) the extent of tubular continuity between the tubules in primary and secondary dentine. b) the structural nature of Tomes' granular layer. c) the extent of tubular branching. Specimens will be embedded in polymethylmethacrylate and the matrix removed with acid and hypochlorite. The casts of the internal structure of dentine will be examined with the scanning electron microscope. Human dentine and the dentine from an experiment model, the rat molar, will be examined. In the former, secondary dentine which formed both physiologically and as a result of various insults will be observed. In the latter, an attempt will be made to determine, in a temporal sequence, the extent to which tubules in secondary dentine are continuous with those in the primary dentine.